Temperature swing adsorption (TSA) units are used in a variety of industries to remove contaminants from fluids, such as liquids and gas streams. TSA is a batch-wise process consisting of two basic steps: adsorption and regeneration. In the adsorption step, contaminants or other impurities are removed from the fluid by adsorption onto a solid adsorbent material and then the treated stream leaves the unit with lowered contaminant levels. In the regeneration step, the adsorbed contaminants are desorbed from the solid adsorbent material by means of a regeneration stream (typically a gas stream).
The regeneration step includes two major parts: heating and cooling. In the heating part of the process, the regeneration stream is heated to an elevated temperature and caused to flow over the solid adsorbent material. Due to the heat of the gas and the difference in partial pressure of the contaminants on the solid adsorbent material and in the regeneration gas stream, the contaminants desorb from the solid material and leave the unit with the regeneration gas. A cooling step is then necessary to condense the contaminant. In the case that the desorbed contaminants in the regeneration gas cannot be removed by condensation (such as CO2 removal), other separation means are employed to separate the contaminants from the regeneration gas, such as membrane or solvent absorption separation. The cooled regeneration gas, which is saturated with the contaminants, can then be recycled to the feed in a closed-loop mode to minimize the loss of the regeneration gas. Alternatively, in an open-loop regeneration mode, the effluent regeneration gas can be disposed of as a fuel gas or by venting instead of returning to the feed stream.
Hence, the most basic form of a TSA process unit consists of two vessels, with one vessel in adsorption mode and the other vessel in regeneration mode. However, depending on the quantity of feed material to be treated as well as the amount of contaminants to be removed from the feed stream, several vessels, which operate in a parallel mode, or in alternating sequences, could be required. In a more complicated form of operation, the regeneration step can also be split over two vessels in a series-heat-and-cool cycles, where one of the vessels would be in the heating step and another would be in the cooling step.
Regardless of whether the system operates in a closed-loop or an open-loop regeneration mode, it is always desirable to have concentrated contaminants in the regeneration gas. Such operation can improve the separation efficiency for the contaminant removal by condensation or by other separation means (such as membrane or solvent absorption separation). Stated conversely, it is more difficult for the contaminants to be removed from a regeneration gas stream with diluted contaminants. As a consequence, the majority of the contaminants will be recycled back to the feed in the closed-loop mode. This mode of operation requires an increase the size of the adsorption unit. Consequently, a larger adsorption unit leads to an increasing regeneration flow. And, a higher regeneration flow through the system further dilutes the contaminant concentration, thus making it more difficult to condense or otherwise remove the contaminant in the cooled regeneration gas stream.
Accordingly, it is desirable to provide TSA systems and associated fluid purification methods that reduce the required regeneration gas flow and consequently reduce the size of the adsorption unit. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.